1. Field of the Invention
The invention relates to hardware design techniques, and more particularly to a circuit system for wireless communications.
2. Description of the Related Art
A wireless local area network (wireless LAN or WLAN) is a cellular network that facilitates communication via radio signals instead of wires. WLANs are used increasingly in both home and corporate environments. Innovations in WLAN technology help people to work and communicate more efficiently. The advantages of high mobility and no need for cabling and other fixed infrastructure have proven to be a boon for many users. Wireless LAN users can use the same network applications as in an Ethernet LAN. WLAN adapter cards used on laptop and desktop systems support the same protocols as Ethernet adapter cards. For most users, there is no noticeable functional difference between a wired Ethernet desktop computer and mobile WLAN workstation other than the added benefit of mobility within the WLAN.
In 1997, the first wireless Ethernet standard, known simply as 802.11, was adopted and published by the IEEE. This unified standard provided several modes of operation and data rates up to a maximum of two megabits per second (Mbps). Work soon began on improving the performance of 802.11. The eventual results were two new but incompatible versions of the standard, 802.11b and 802.11a. The “b” version operated in the same frequency range as the original 802.11, the 2.4 GHz Industrial-Scientific-Medical (ISM) band, but the “a” version ventured into the 5 GHz Unlicensed National Information Infrastructure (U-NII) band. 802.11b mandated complementary code keying (CCK) for rates of 5.5 and 11 Mbps, and included as an option Packet Binary Convolutional Coding (PBCC) for throughput rates of 5.5 and 11 Mbps, and additional range performance. 802.11a turned to another multi-carrier coding scheme, Orthogonal Frequency Division Multiplexing (OFDM) achieving data rates up to 54 Mbps. In June of 2003, IEEE announced its final approval of the IEEE 802.11g standard which adopted a hybrid solution that included the same OFDM coding and provided the same physical data rates as 802.11a. Nonetheless, 802.11g occupied the 2.4 GHz band of the original 802.11 standard.
Designing the circuit of any system containing radio frequency (RF) signals is always critical and challenging. As data rate increases, printed circuit board (PCB) layout becomes more complex especially for compact devices, such as 802.11a/b/g MiniPCI or PCMCIA cards. In order to achieve the benefits offered by these devices, particular attention must be paid to the requirements of circuits that will be more sensitive in higher frequencies. An unsatisfactory design may otherwise lead to technical problems in the WLAN devices, manifesting itself in reduced coverage or data throughput. Therefore, what is needed is a circuit design for use in WLAN systems, which addresses some of the above mentioned and other problems of the related art.